Ultrahigh-frequency mixer



Dec. 29, 1953 s. ROBERTS ULTRAHIGH-FREQUENCY MIXER Filed June 23, 1945 EOF lNvENToR SHEPARD ROBERTS ATTORNEY Patented Dec. 29, 1953 UNITEDSTATES ATENT OFFICE Application June 23, 1945, Serial No. 601,160

(Cl. Z50- 20) Claims.

This invention relates to ultrahigh frequency mixers, particularly thosewhich operate directly in a Wave guide and which may be tuned to matchthe impedance of the connecting guide at the operating frequency.

It is an object of this invention to provide a mixer which operatesdirectly in a wave guide.

It is a further object of this invention to provide a mixer which may betuned to match the impedance of the connecting wave guide at theoperating frequency.

It is a further object of this invention toprovide a mixer which mixestwo extremely high frequencies to produce a relatively low intermediatefrequency which may be easily amplified. Y

It is a further object of this invention to provide a mixer which uses acrystal with the accompanying reduction in noise level.

1t is a further object of this invention to provide a mixer Whosecrystal may be easily exchanged with another. f

It is a further object of the invention to provide a mixer utilizing acrystal inserted in a wave guide which crystal is directly connected toan intermediate frequency amplifier.

Other and further objects will appear during I 'the course of thefollowing description.

Broadly, the invention embraces a crystal of the cartridge typepositioned transverse to a vwave guide in the plane of the electricfield. One

end of the crystal cartridge is connected directly to the adjacent wallor the guide. The other end is connected to the adjacent wall oppositeto iirst mentioned wall through a circuit effectively series resonant atthe frequencies of the local oscillator and signal. This circuit permitspassage of the signal and local oscillator currents, but will not permitpassage of the intermediate frequency current. A direct connection isprovided for this intermediate frequency at the end of the crystalassociated with the resonant circuit to the input of the intermediatefrequency amplifier. i

A movableplunger is provided in the wave guide which in cooperation withtwo screws movable in the electric plane of the guide match the portionof the guide afsociated with the crystal cartridge of the remainingconnecting portion of the guide.

The invention will now be described in detail ywith reference to theaccompanying drawings,

in which:

Fig. l is a generally sectional elevatlonal view or the mixer andassociated radio frequency circuit; i

Fig. 2 is a sectional elevational View of a Joint for adjusting thelength oi the wave guide 1n Fig. 1.

in Fig. 1 is shown an arrangement of apparatus 60- for carrying out thepresent invention which is particularly adapted for transmitting and receiving systems in which hollow pipe wave guides are used for thetransfer of oscillatory energy from one part of the system to another.Such an arrangement is consequently of particular utility at the shorterwave lengths and in apparatus where high transmitter power is employed.The .hollow pipe wave guide leading from the transmitter to the antennasystem is shown at 5U. This and the other v'ave guides of the system areusually provided in rectangular form, although cylindrical wave guidescould also be used, because the rectangular form of wave guide givesgood control over the polarization of the transmitted waves. A branchwave guide 5| forms a junction with the wave guide 5B at 52. The variouswave guides in Fig. l are shown in a section parallel to the directionof the electric vector, which is to say, in accordance'vvith wave guidedesign practice. they are shown in a longitudinal section parallel tothe shorter wall of the wave guide. The junction 52 is therefore one ofthe type known as an electric plane junction. It is to be understoodthat a magnetic plane junction could also be used, in which case theaxis of the wave guide would have a direction perpendicular to the planeof Fig. 1 and. the iunction 52 would open into a narrower Wall of thewave guide 5i] instead of into one of its broader walls.

The wave guide 5l leads to an automatic electric breakdown dischargedevice 53 provided with a resonator 54 having a discharge gap 55. Theresonator 54 is provided with a flexible wall 56 ywhich permits'adjustment of the dimensions of the gap 55 and. consequently of theresonant frequency of the device by means of a rod 51 and a screw threadadjustment 58. Coupling between the input and output wave guide and theresonator 5s is provided simply by holes in the resonator walls whichclose oi the respective wave guides, which coupling holes are providedwith sealed-in glass windows 59 for the purpose of maintaining a partialvacuum in the resonator 5i. The partial vacuum is originally establishedthrough an exhaust tube 5t. which is sealed oir, as at 5l, after theevacuation. The exhaust tube also serves for the support of a keep aliveelectrode 62. A small glass bead 53 is mounted. on the electrode 52 toprevent accidental shortcircuiting of the electrode voltage and toassist in centering the electrode in the structure.

In order to reduce dissipation of transmitter power of the gap 55 thelength of wave guide lil should be properly adjusted. rihe length ofvthe wave guide 5l indicated by the dimension a should closelyapproximate an even number of half-Wave lengths for best results, with asmall adjustment (usually shortening the length slightly from that justprescribed) on account of the vloading effect of the coupling aperturebetween accesos the wave guide 5l and the resonator 5s. It will be notedthat the proper length of a hollow pipe vavo guide between, a wave guidejunction and an electrical oreal Town switch differs from the desirablelength between a coaxial conductor line junction and an automaticelectrical breakdown switch The resonator 5e is coupled through theother of the windows 5s to a wave guide t5 leading towards the receiverinput. In the apparatus of l the function of a resonator apparatus iSperformed by the end portion of the wave guide lili in the neighborhoodof the crystal Se, which portion is caused to act as a resonant sectionof wave guide, the characteristic impedance .of the non-resonant part ofthe wave guide 65 being matched to the resonant section of wave guidewhich includes the crystal, by means of a suitably located loadingcapacitance as hereinafter described. Such apparatus may be said tofunction as a resonant transformer between the crystal and non-resonanttransmission means. This view is only accurately descriptive lwhen theimpcdances oi the system. are fairly well matched, by the arrangement,for otherwise the transmission means connected to the transformer willhave standing waves and will not act as a non-resonant line.

The crystal i355 which operates as a iirst or heterodyne detector islocated between a clip 5to and an adjustable screw-capped recess el,thus being essentially across the wave guide S5. The crystal is shown inthe form of a cartridge of the type commonly used for mounting microwave detector crystals, which contains the usual silicon crystal, catsWhisker wire and elec trical connections, the structure being sealed inand enclosed in an insulating structure having terminal contact caps.This form of structure is adapted to preserve Ythe crystal contactadjustment against disturbance from shock. llhe clip ec is hollow inOrder to receive the crystal and is provided with slots such as thoseshown at 52 in order to provide spring action for better Contact withthe crystal. is insulated from the wave guide structure by a largeinsulating plug 69 and a thin insulating washer T3. A direct connectionis made from. the clip to the ungrounded side of the input of theintermediate frequency amplifier' of the receiver (not shown), theelectrical connection being efected by means of the rod 1| and the wirel2. Although for purposes of clearer illustration the washer 'it appearson the drawing as having a substantial thickness, in fact this washer inpractice is extremely thin and may for instance be made by stamping outof polystyrene tape of a thickness of only five thousandths (.005) of aninch.

The close approach of the structure 'il to the structure across the thinpolystyrene washer 'lll provides a by-pass condenser across theintermediate frequency amplifier input which by its filtering actiontends to prevent any signal or local oscillator frequency currents whichmay reach the neighborhood of the washer lli from going on toward theintermediate frequency cir cuits. The by-pass capacitance so provided istoo small to have any appreciable effect upon the intermediateYfrequency output of the mixer stage.

Although the by-pass capacitance just described can serve to filter theintermediate fre quency output of the mixer it is too far from thecrystal to provide the short and direct signal frequency connectiondesired between the end of The clip 66a by byJ-pass resonator.

the crystal cartridge engaged in the clip 65o and the wave guide wall.The latter eiect is obtained by surrounding the clip 66a by a resonatorsuch that a short circuit for such frequency appears by reflection atthe crystal end of the clip, which is to say that the resonator presentsan extremely low impedance between the clip and the wave guide wall forits resonant frequency. Such a resonator may be designated as Thespecial form of resonator used for radio frequency by-passing is .formedby providing a circumferential space about the clip 55a and dividingthat space by a flanged cylinder lt, the ilanged end of which forms part.of the wave guide wall e5 and is in good electrical Contact with thestructure As shown on Fig. l this results in providing a cylindricalspace which at a certain distance from the point where it opens up intothe wave guide is folded back .on itself and terminates in a closed end`at lli. The point where this space or cavity is folded back on itselfis made to approximate very closely a quarter-wave length of theoscillations of microwave frequency upon which the device is to operate,which is to say that the dimensions shown at b on Fig. 1 shouldapproximate a` quarter-wave length of such oscillations. The closed endof the cavity at 'l5 will then appear at the mouth of the cavities whichsurround the extremity of the clip 56a as a very low impedance,practically a short circuit, since the mouth is spaced electrically ahalf-wave length away from the closed end l5. In addition theconguration of this bypass resonator is such that the nature of theelectrical insulation between the rod 'il and the structure 'i3 atpoints beyond the folded end of the resonator -becomes quite immaterialto the radio frequency operation of the crystal circuit. As a result cithe operation of the icy-pass resonator the crystal is effectively, forthe microwave frequencies in question, .connected directly across thewave guide 55.

The end of the wave guide t5 beyond the crystal location is closed offby a conducting plug or plunger l5. This plunger lli is provided on itsupper and lower faces with bypass resonators such as those described inconnection with the clip @6a. Since the configuration of the wave guideis, as is the usual case, rectangular, and since the by-pass resonatorsare in such a case useful only between the plunger and the broader sidesof the wave guide (the electric vector being perpendicular to thebroader side), the bypass resonators are rectangular in configuration inthe case or" the plunger l instead of cylindriu cal as shown inconnection with the clip @Ba and the structure i3. The byepassresonators are shown in the plunger 'l5 at ll. As in the case ol theby-pass resonator in the structure 'E3 surrounding the clip thedimension marked b on Fig. 1 should closely approximate one quarter ofthe wave length of the oscillations in question. When constructed asdescribed the plunger 'i5 acts to close off the wave guide 65 at theplane of its front surface 'i8 with the practical eifect of a perfectlyconducting terminating wall, irr^ speotve of the quality of the contactbetween the plunger 'l and the wave guide E5 rearwardly of the by-passresonator` ll.

Motion oi the plunger.: l5 in or out the wave guide 55 will change thepattern o the standing waves produced as a result of reflection ofoscillations from the termination of the wave guide at the surface i8,so that by adjustment of the position of the plunger le the impedance ofthe oscillating system at the point where the crystal is connectedacross it may be made to match the impedance of the crystal or tocorrespond to some slightly higher value, providing a factor of safetyagainst overload.

In order that the resonant end portion of the wave guide 65 whichincludes the crystal and its associated structure may be coupled to thesignal input for maximum energy transfer of the received signal duringperiods when the transmitter is not operating, which requirement usuallycorresponds to the requirement that there shall be no standing waves inthe portion of the wave guide 55 immediately adjacent to the electricaldischarge device et, two adjustable capacitance loading devices 853 andSi are provided in the wave guide 65 at particular locations between thecrystal position and the electrical discharge device 53. The loadingdevices comprise rods movable in and out of the guide and extendingthrough the middle portion of the wave guide wall and parallel to theelectric vector. Variable inductances may be provided in a similarfashion by orienting rods 86 and 3i perpendicularly to the electricvector. The rods when providing variable inductance, in the case ofrectangular guides, would then usually be introduced through one of thenarrower walls. Because crystals usually differ quite widely from eachother in radio frequency impedance, a suiiiciently wide range matchingadjustment for practical use cannot be made with a single adjustablecapacitance at a xed location. A single adjustable matching capacitancesuch as the structure 8|, 83 could be mounted in a fashion permitting itto be slid longitudinally along the wave guide 55, which could besuitably slotted for the purpose. Al prefer, however, to provide twoadjustable matching capacitances, separated by a distance equal to aquarter wave length of the oscillations inthe guide (as indicated by thedimension c on Fig. l), so that if a suitable match cannot be obtainedwith any adjustment of one of the capacitances, it is practicallycertain to be obtainable with some adjustment of the other adjustablecapacitance. One of the adjustable capacitances is thus preferably keptilush with the wave guide as shown by the position of the capacitancescrew gli.

The capacitances loads tt and 3i are essentially screws protruding intothe wave guide 65 at suitably selected points. The structures 82 and 83in which the screws 8i) and 8i are respectively threaded and which arein electrical contact with the wall of the wave guide S5 are providedwith by-pass resonators similar to those previously described inconnection with the structure i3 and in connection with the plunger it,which here serves the function of establishing an eifective radiofrequency connection directly between the screws 8!) and si and theimmediately adjacent portion of the wall of the wave guide 55. Thus agood radio frequency electrical contact Vis maintained at the desiredpoint between the capacitance load and the wave guide wall, irrespectiveof the quality of electrical contact occurring at the screw threadsassociated with the capacitance loading devices. This is a greatadvantage since the electrical contacts at such screw threads are oftenuncertain and sparking might otherwise occur. The by-pass resonators inthis case have i a cylindrical conguration'similar to that oftheicy-pass resonator associated with the structure i3 surrounding thecrystal clip tba. As before,

the dimension of these resonators marked on Fig.

1 'as b should closely approximate one quarter oi' the wave length ofthe oscillations in question.

The distance between the axis of the crystal 6E and the nearer matchingscrew 3 I, shown on Fig. l by the dimension d, is not critical withinwide limits, since variations therein can usually be compensated byadjustment of the particular matching screw which is used. Distancesless than one-half wave length are to be preferred in order to minimizefrequency sensitivity. It is to be noted that the continuation of thewave guide beyond the crystal it and the adjustable termination 'it inefiect constitute a variable admittance across the wave guide e5 at thecrystal position. The tuning screws @il and si likewise constitutevariable admittances across the wave guide 65. The adjustment of theterminating wall i8 and of one of the screws si), il may be performed inaccordance with the practice relating to double stub tuners for thepurpose of matching the impedance of the crystal to the characteristicimpedance of the wave guide B5. Also in accordance with the practice inconnection with double stub tuners, a spacing between the variableadmittances of approximately threeeighths wave length is preferred, sothat the distance d indicated on Fig. l between the crystal axis and theaxis oi the tuning screw 8i is preferably niade approximatelythree-eighths or onethird wave length. This dimension may be variedrather widely, however, the only limitation being that a spacing betweenthe crystal axis and one of the tuning screws equal to a half wavelength would make the tuning screw in question useless, since a doublestub tuner with onehalf wave spacing between stubs would require stubscapable of kadding infinite susceptance in order to fulfillits purpose,a condition which cannot generally be met in practice.

The matching arrangement comprising the acl- `justa-ble closure i8 andthe adjustable capacitive loads 8i! and Si is somewhat different fromthe conventional double stub tuner to which an analogy has just beendrawn for the purpose of illustration and explanation, one of the tuningfull control over the matching of reactances it is desirable to providea second capacitive load a 'quarter-wave length distant from the nrstcapacitive load. Ordinarily the matching adjustment Ais made byadjusting the plunger and one of the screws 8B, 8i, the other screwbeing left in a retracted position such as that of the screw 8 in Fig.1.

Inbrderthat the crystal may function as a -heterodyne detector or mixerit is necessary to Vfeed `to the crystal a locally generated oscillationas well as the signal picked up by the antenna system. ln the apparatusof Fig. l the local oscillator output is coupled to the wave guide n35by extending the central conductor Sii of the coaxial output line 86 ofthe local oscillator so that the conductor protrudes into the wave guide85 and is thereby adapted to excite oscillations in the wave guide 85which will be transmitted along the wave guide to the crystal. ln orderto mitigate transfer of energy from the local oscillator to theresonator 5 tern and out into s conductor where it prets-des into thewave guide is so arranged t iat the distance between it and theapparatus which distance is shown on Eig. 1 by ion is apuro iately anodd number of quarter-wave lengths or the oscillations in dues-tion,thus mismatching the oscillator output for transfer of energy toward thearitenna and roitigating undesired radiation.

For the annication o the present invention to the arrangement ci aoaratus shown in Fig. l the apparatus should be so constituted that thedistance between the crystal and the outnut side oi the paratus dit,which distance is shown on Fig. l the dimension f, will approximate anodd rn aber of cnie.rter-wave lengths oi the oscillations in question,subieet to allowances lor terminal eiects lssed ber-ow. in the apnaratusoi' Fig. 1 no arrange-.nient is shown for adjusting the nsion ,f and isexpected that the frequency of onerat n will he suniciently well 'Encanin advance oi manufacture that the proper dimension j be incorporatedinto the design of the atus. Ii the frequency of operation is not knownto a su ent degree oi accuracy for the obtaining or a o ension fsuitable to achieve the advantages or" this invention in the fullestdegree, inechai cal arrangements could be provided in the porti ,n ofthe wave `cuide et adjacent to the annsratus i'or varyu ing the waveguide l h. Such an arrangement could be a sliding' jor-.1', prefer ablyone provided with a by-pass resonator as show?` in Fig. 2 andhereinafter described, which would eliminate the necessity for extremelygood electrical contacts. The exact magnitude of dimension is sub- ;ectto a slight correction in the oi the apparatus oi 1 would be a snghtdecrease in the length on account of the 'loa-ding eiect o the couplingeve 1re between the wave guide t and the reson Tl s correction is 1.tively slight and it may be estimated by known methods either throughcalculation or experimental deterrnination. A more important factor .leactual dimension j used in prace crystal cartridge dii dimension f. Thecalca? eiiects can be av the dimension f is deterrnined by direct suchas by measurement or the standing waves in the wave e5 for ci .f mountsor" crystal current.

It is to have heretorcle seen described in terins lenga-s are not te bere erred to the space wave lengths of the oscillations in question, 'outrather to the wave lengths oi tie oscillations in the structure inquestion. Where t1 e structure in question is a wai/'c guide oi rnowncross section, the wave length oi the oscillations within the wave guidereadily be calculated by known formulae ai .l or" course may also beexperimentally determined. The wave length in two conductor lines isaiected by such factors as the number and sind of spacing insulators.Formulas for the wave length in 'various types o line are well known.The wave length to which the dimension shown on Fig. 1 as small b refersis related to a somewhat more complicated struc ture, namely, the bypassresonators above scribed. These resonators operate in the coaxial modeand the wave length is substantially the free space wave length, itbeing desirable,

tion of these terminal however, to maire a small allowance for the endeffect at the mouth of the resonator in calculating the length of theresonator. The bypass resonators 'il operate in the rectangular waveygui-:le mode and the electrical quarter-watlength diinension b shouldconsequently be physically somewhat longer than the electricalquarter-wave length dimension b, being almost one quarter of the wavelength in the guide o5 (but not quite that great, because of the lesserwidth of the resonators 51).

As shown in Fig. 1, the spacing of the electrical line length accordingyto this invention bett-'eeen the protective breakdown switch and thereceiver input may be provided Jfor in the design of the apparatus whenthe apparatus is intended to be used at a single frequency, withouti...- corporating :means for adjusti; g the said stocing. if it isdesired to incorporate into arp tus of the general connguratiol. shownin rig. l some means for adjusting the spacing in acn cordance withchanges in operating frequency, this be done by providing a s ng jointin the pipe wave 3 de as above gesteld. A preferred type of slidingjoint for the provision of such an adjustment is illustrated in i g.

in Fig. 2 the two portions of rectangular pipe wave guide between whichthe sliding joint is arranged are shown at Sii and si in a cross sectionparallel to the electric Vector of the o 'll intended to be transr.itted. The Si is vided with a widened extremity 52 adapted t over thepine Q8 leaving a small clearanc ceti-reen the upper and between thelower Shallow cavities lower sides or" the pipe Si? (i. e. its broaderwhich are covered by conductinfT partitions except tor a narrow slot SSalong the forward end of each cavity where the said cavities communicatewith the clearance space center lines of slots 9E are spaced an electquarter-wave length from both the end oi pipe sa and from the rear walloi associated cavity Such electrical quarter-wave length correspondsapproximately7 to the dimension on Fig. 1.

The cavities Sii-i are closed orf at the sides by the lateral Walls ofthe pipe 9G which also provides support for the cover plates 95. Theplates S5 are preferably soldered onto the pipe wave guide 90. Beads Siand @8 are provided on the wave guide extremities to maintain theclearance $3 between the upper walls and between the lower walls or" thewave guide pipes and to assure the absence of electrical contact atpoints located between the slots SS and the immediate neighborhood ofthe end of the wave guide it. The beads 97 need not be continuous ridgesand may be replaced by simple guide studs near the corners of the waveguides or at intervals across the wave guide walls along a lineperpendicular to the Wave guide axis.

The cavities 94 cooperate with the clearance space S3 to constituteoy-nass resonators and to produce the equivalent of a very goodelectrical contact between the end of the pipe 8! and the wall of thepipe 9! for electric oscillations of frequencies approximately equal tothe frequency of operation.

Although I have shown and described only a certain specific embodimentof the invention, am fully aware of the many modications possiblethereof. While there has been described what is at present consideredthe preferred embodiment of the invention, it .will be obvious to thoseskilled in the art that various changes and modiilcations may be madetherein that fall within the scope of the appended claims.

Iclaim: o

1. A mixer adapted to use a crystal cartridge, comprising a wave guidehaving diametrically opposed openings in its walls, a hollow structureextending through one of said openings and projecting outwardly fromsaid guide, a rod projecting through said hollow structure having a clipadjacent the guide for holding one end of said crystal cartridge, ascrew cap covering the other of said openings, and adapted to connectthe other end of said crystal cartridge to the adjacent wall of saidwave guide, adjacent abutments on the inside of said hollow structureand on said rod, a layer of polystyrene tape separating said abutmentsto form a by-pass condenser therebetween, a plug threadably connected tothe inner wall of said hollow structure pressing against the abutment onsaid rod and insulated therefrom to secure said rod in said hollowstructure, a cylindrical sleeve positioned between said clip and saidhollow structure and spaced from a flange on one end of said sleeve andconnecting said sleeve to said hollow structure adjacent the wall ofsaid guide, said sleeve being in length substantially one quarter thewave length of the energy to be mixed and thereby eiectively providing ashort circuit between said l clip and the adjacent wave guide wall forsaid energy.

2. In combination, a wave guide. means for providing reactance inparallel with said guide comprising, a rod extending into said guidethrough a circular opening in a side wall of said guide, said openingbeing of a' diameter substantially larger than that of said rod, acylindrical hollow structure attached to said guide and concentric withsaid opening in said guide, a

,cylindrical sleeve disposed concentrically between said rod and saidhollow structure and yspaced from both, a ilange on one end of saidsleeve and electrically connecting said sleeve to said hollow saidguide, the inner diameter of said cylindrical hollow structure beinggreater than the outer diameter of said sleeve, said sleeve being inlength substantially one quarter the wave length of the energy beingtransferred in said guide and thereby effectively providing a shortcircuit at said opening in said guide Ior said energy.

3. In combination, a wave guide, means for providing reactance inparallel with said guide comprising, a plurality of rods extending intosaid guide through circular openings in a side wall of said guide, saidrods being spaced longitudinally of said guide an odd number of quarterwave lengths, said circular openings being of diameters substantiallylarger than the diameters of said rods, a plurality of cylindricalhollow structures attached to said guide and concentric with saidopenings in said guide, cylindrical sleeves disposed concentricallybetween said rods and said hollow structures and spaced from said rodsand said hollow structures, flanges on one end of each of said sleevesand connecting said sleeves to said hollow structures adjacent to saidside wall of said guide, the inner diameters of said cylindrical hollowstructures being greater than the outer diameter of said sleeves, saidsleeves being inn length substantially one quarter the wave length ofthe energy being transferred in said guide and thereby eiectivelyproviding structure adjacent to the wall of short circuits at saidopenings in said guide for said energy.

4. A mixer adapted to use a crystal cartridge comprising, a wave guidehaving diametrically opposed openings formed in the walls thereof, ahollow structure attached to said wave guide at one of said openings andprojecting outwardly from said guide, means within said hollow structurefor retaining one end of said crystal cartridge, a rod connected to saidmeans and extending outwardly beyond said hollow structure, a cap forcovering the other of said openings and adapted to connect the other endof said crystal cartridge to said wave guide at the adjacent wallthereof, a flange on said rod, a stepped section within said hollowstructure of diameter smaller than that of said hollow structure andthat of said ange, a layer of dielectric material separating said ilangeand said stepped section to form a bypass condenser therebetween, meansfor retaining said flange in close contact with said dielectric layerand said layer in close contact with said stepped section, and means atthe junction of said wave guide and said hollow structure for providingan eiective short circuit at said -junction to energy being transferredin said wave guide.

5. A mixer adapted to use a crystal cartridge comprising, a wave guidehaving diametrically opposed openings formed in the walls thereof, acoaxial output line attached to said wave guide at one of said openingsand projecting outwardly from said guide, a conductive cap for coveringthe other of said openings and adapted to connect one end of saidcrystal cartridge directly to the wall of said wave guide adjacent theother of said openings, an inner conductor within and forming a part ofsaid coaxial output line having a flange rformed thereon, means forretaining the other end of said crystal attached to said inner conductoradjacent said one of said openings, an outer conductor forming theexternal surface of said coaxial output line and having a section ofreduced diameter adjacent said ilange, a layer of dielectric materialbetween said flange and said section of reduced diameter forming acondenser therebetween and means at said one of said openings in saidwave guide for presenting an effective short circuit to energy beingtransferred within said wave guide.

SHEPARD ROBERTS;

References Cited in the file of this patent UNITED STATES PATENTS NumberV Name Date 1,537,856 Michels May 12, 1925 2,236,004 MacLean Mar. 25,1941 2,239,905 Trevor Apr. 29, 1941 2,253,589 Southworth Aug. 26, 19412,257,783 Bowen Oct. 7, 1941 2,332,952 Tischer Oct. 26, 1943 2,378,944Ohl June 26, 1945 2,408,420 Ginzton Oct. 1, 1946 2,413,186 La Rue Dec.24, 1946 2,418,518 McArthur Apr. 8, 1947 2,424,002 Sloan July 15, 19472,427,087 Carlson Sept. 9, 1947 2,427,107 Landon Sept. 9, 1947 2,436,8304Sharpless Mar. 2, 1948 2,460,109 Southworth Jan. 25, 1949 2,469,222Atwood May 3, 1949 2,514,678 Southworth July 11, 1950 FOREIGN PATENTSNumber Country Date Australia Nov, 4, 1942

